Retransmission in data communication systems

ABSTRACT

Embodiments related to retransmission in data communication systems are described and depicted

REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the priority date of U.S.provisional application 60/976,808 filed on Oct. 2, 2007, U.S.provisional application 60/984,162 filed on Oct. 31, 2007 and U.S.provisional 60/991,809 filed on Dec. 3, 2007, the contents of which areherein incorporated by reference.

BACKGROUND

Modern data communication systems such as DSL communication systemstransmit a plurality of different data types. Data of high-qualityservices such as IPTV services or video services require an efficientnoise protection since missing data often provide strong disturbances ofthese services. Present impulse noise protection with Reed Solomoncoding and interleaving provide not sufficient protection for thesehigh-quality services.

Retransmission schemes have been introduced to address noise protectionfor high-quality services. In retransmission, data transmitted over acommunication link such as a subscriber line is stored at thetransmitter site for some time. In case the receiver site receivescorrupt data, for example when an impulse noise occurs, the transmittersite retransmits the data based on a request from the receiver to againover the communication link.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows a schematic block diagram of a communication layer model;

FIG. 2 shows a schematic diagram according to an embodiment of thepresent invention;

FIG. 3 shows a chart diagram according to an embodiment of the presentinvention;

FIG. 4 a shows a schematic embodiment of the present invention;

FIG. 4 b shows a schematic embodiment of the present invention;

FIGS. 5 a and 5 b show a protocol stack according to an embodiment ofthe present invention;

FIGS. 5 c and 5 d show a protocol stack according to an embodiment ofthe present invention;

FIGS. 6 a to 6 c show examples of fragment headers; and

FIGS. 7 a and 7 b show a protocol stack according to a furtherembodiment of the present invention.

DETAILED DESCRIPTION

The following detailed description explains exemplary embodiments of thepresent invention. The description is not to be taken in a limitingsense, but is made only for the purpose of illustrating the generalprinciples of embodiments of the invention while the scope of protectionis only determined by the appended claims.

In the various figures, identical or similar entities, modules, devicesetc. may have assigned the same reference number.

In the following various embodiments of a retransmission system aredescribed. The embodiments are described with respect to a DSL systemsuch as an ADSL or VDSL system. However, it is to be understood that thevarious embodiments may also be implemented in other data communicationsystems for providing retransmission.

For better understanding, in the following an exemplary protocol stackof a present VDSL or ADSL system is explained with respect to FIG. 1.FIG. 1 shows the lowest two layers in the OSI model, i.e. the PHY andthe data link layer. According to FIG. 1, the PHY layer (first layer inthe OSI model) is divided into three layers or PHY-sublayers. The firstlayer is the PMD (physical media dependent) layer including basicfunctionality such as symbol timing generation and recovery, encodingand decoding, modulation and demodulation, echo cancellation (ifimplemented) and line equalization, link startup, and physical layeroverhead (superframing). Additionally, the PMD layer may generate orreceive control messages via an overhead channel.

The next PHY-sublayer is the PMS-TC (physical mediaspecific-transmission convergence) layer which is connected to the PMDlayer through the δ interface. The PMS-TC layer is a management planeand provides management primitive indications to management entities inthe CO and CPE modems. The PMS-TC layer provides in additionfunctionality such as generation of frames and synchronization offrames, (de)scrambling, Reed-Solomon coding and interleaving. The thirdPHY-sublayer is the TPS-TC (transmission protocol specific-transmissionconvergence) layer which is connected to the PMS-TC layer through aα-interface (alpha-interface) at the Central Office Site or aβ-interface (beta-interface) at the subscriber site. The TPS-TC layerprovides functionality such as packetizing into frames, organizing ofthe bearer channels, multiplexing. The TPS-TC layer is connected to thedata link layer (layer 2 in the OSI model) by the γ-interface(gamma-interface).

While the above described existing DSL layer model does not provide aretransmission functionality or retransmission layer, embodiments of thepresent invention address the provision of a retransmissionfunctionality or retransmission layer for a DSL transmission system.According to one aspect, a retransmission functionality is provided fora DSL transmission system by providing a retransmission sublayer (whichmay sometimes be referred to as retransmission layer) above at least onesublayer of the TPS-TC layer. According to embodiments, theretransmission sublayer may be located above the 64/65-octetencapsulation sublayer of the TPS-TC layer and below the data linklayer. Furthermore, according to embodiments, the retransmissionsublayer may be provided at the gamma interface and below the data linklayer. According to one embodiment, the retransmission sublayer may beprovided between the 64/64-octet encapsulation sublayer and a bondingsublayer.

In embodiments, the basic retransmission unit is a fragment of a packet.In other embodiments, the basic retransmission unit is a group offragments of a packet. Therefore, in embodiments, a fragment of a packetor a group of fragments of a packet are stored in a retransmissionbuffer to allow retransmission of a fragment or a group of fragment.

Retransmission at the gamma interface or above at least one sublayer ofthe TPS-TC layer allows according to one embodiment to make reuse ofexisting bonding sublayer functionality in case of bonding andnon-bonding applications, i.e. reuse of PAF (Packet AggregationFunction) for the 64/65-octet TPS-TC sublayer.

Furthermore, retransmission schemes at the gamma interface or above atleast one sublayer such as the 64/65 octet encapsulation layer avoidsproblems occurring in implementations of retransmission schemes belowthe gamma interface. For example retransmission in the PMS-TC layer orbelow is based on a continuous data stream since TPS-TC sublayer appliesrate decoupling. If data is missing from the upper sublayer, idle bytesare inserted in case of 64/65-octet TPS-TC sublayer. This means thatretransmission will be done also for idle data carrying no information.In case of retransmission above sublayers of the TPS-TC layers or at thegamma interface the useless retransmission of rate decoupling data canbe avoided.

Furthermore, retransmission schemes in the PMS-TC layer or at the alphainterface may have a negative effect on the bonding sublayer sinceretransmission of one line in the bonding group increases thedifferential delay for the bonding sublayer. Line specificretransmissions lead to a differential delay variation for the bondingsublayer and it is not known by the bonding sublayer when it has totolerate which differential delay due to retransmission. If theretransmission sublayer is placed at the gamma interface bonding &retransmission sublayer can in an embodiment be combined so that thisproblem can be overcome.

Retransmission at gamma interface can realize service specificretransmission also with one latency path or bearer channel. The servicespecific retransmission has the advantage that a retransmission overhead(e.g. sequence numbering) has to be taken into account only for theservice which may be protected but not for other services which are notprotected by retransmission for example low priority services. Since noadditional overhead is required for the services which are not protectedthese services do not take away line bandwidth for retransmission.Additionally, the bandwidth of a non-retransmission service withvariable bit rate (e.g. data service) may be used during retransmission.This may reduce or even obsolete the need to foresee an overhead in thebandwidth of the retransmission service.

A retransmission scheme at the gamma interface can be implemented in aPHY connected network processor which gives the advantage that usuallythe buffer or memory limits are more relaxed than for a PHY memory.Additionally the network processor can provide advantages for a servicespecific retransmission scheme since service classification is also donethere.

Furthermore, according to one aspect of embodiments, existing bondingsublayer functionality is reused also for the retransmission sublayer.For example, embodiments of the pre-sent invention implement a64/65-octet TC sublayer with a fragmentation function, sequencenumbering function of the bonding sublayer called PAF (PMA AggregationFunction=Physical Medium Attachment Aggregation Function) and OAM(Operation Administration and Maintenance) insertion & extractionfunction of the bonding sublayer called BACP (Bonding AggregationControl Protocol). These functions are provided for providing bondingfunctionality but can be reused for providing retransmissionfunctionality as will be described in more detail below. PAFfunctionalities are for example described in IEEE 802.3ah-2004 and BACPfunctionalities are described for example in the Draft Amendment 2 toITU Recommendation G.998.2, June 2007.

Each fragment or a group of fragments may contain retransmissionspecific information such as first information indicating whether thefragment or the group of fragments contains retransmitted data or doesnot contain retransmitted data. The retransmission specific informationmay be provided in an additional header field appended to the existingheader. The additional header field may be of the size of one byte.Furthermore, each fragment or each group of fragments may contain secondinformation related to retransmission indication, for exampleinformation indicating how many times the retransmitted data has beentransmitted prior to the current retransmission. For example, theretransmission indication may indicate that the retransmission data areretransmitted for the first time, the second time or a nth time.Furthermore, information related to the different categories of the datastreams (priority or class of service) may be provided in the additionalheader field.

According to embodiments, the retransmission is based on a sequencenumber information of the last correctly received fragment.

The sequence number information may be included in a retransmissionrequest generated and transmitted to the transmitter when the receiverdetects a corrupt received fragment, for example due to the start of anoise impulse. The retransmission request may be repeated as long as noretransmission data has been received by the receiver.

Furthermore, in the direction from the subscriber to the CO (CentralOffice), a retransmission request channel may be provided by using theadditional header field described above. Rate decoupling may be providedfor the request channel.

According to embodiments, the retransmission sublayer is separated fromthe bonding sublayer and provided between the bonding sublayer and64/65-encapsulation in the TPS-TC sublayer. A rate decouplingfunctionality may be provided in the retransmission sublayer such thatidle fragments of a new category (which are hereinafter referred to asspecial idle fragments) are inserted and removed in the retransmissionsublayer. The special idle fragments are however not identified as idlefragments by the TPS-TC layer. Therefore, the special idle fragments aretransparent to the TPS-TC layer and are not removed at the TPS-TC of thereceiver site but are transferred to the retransmission sublayer wherethe information contained in the special idle fragments can be analysedfor gaining retransmission information such as a sequence numberinformation of the fragment. The special idle fragments are then removedat the retransmission sublayer.

A sequence number scheme is provided for identifying the fragmentscontaining user data (user data fragments) as well as the special idlefragments. The sequence number scheme reuses the sequence numberfunctionality provided by the bonding sublayer for the user datafragments together with a sequence number functionality provided at theretransmission sublayer.

According to one embodiment, the special idle fragments are used fortraining or determining one or more repetitive noise parameters such asREIN (repetitive electrical impulse noise) parameters. The one or morerepetitive noise parameters may then be used to determine time periodsduring which repetitive noise is expected. During the determined timeperiods of repetitive noise, no user data may be transmitted. Accordingto one embodiment, instead of user data the special idle fragments aretransmitted during the determined time periods.

To determine the repetitive noise parameters, a plurality of specialidle fragments is repeatedly transmitted from the transmitter to thereceiver, wherein each of the special idle fragments comprises asequence number. One or more sequence numbers of corrupted special idlefragments are identified at the receiver and one or more repetitivenoise parameters based on the identified sequence numbers aredetermined. According to one embodiment, information related to a startand end of a repetitive impulse is transmitted from the receiver to thetransmitter and the repetitive noise parameters are determined based onthe transmitted information.

The repetitive noise parameters determined may be periodicity and lengthof the repetitive noise. The above determining of repetitive noiseparameters may be performed once after link start-up or may berepeatedly performed during showtime.

Referring now to FIG. 2, an exemplary DSL communication system 100 isshown. As is known to a person skilled in the art, the DSL system 100may be a DMT (discrete multitone) system wherein data are modulated onplurality of subcarriers such that each subcarrier is associated withone carrier frequency. The DSL system comprises a first transceiver unit102 a provided at the operators site in an unit 104 such as a centraloffice, a cabinet or other optical network termination units. The firsttransceiver unit 102 a is coupled to a second transceiver unit 102 b viaa subscriber line 106. The second transceiver unit 102 b is integratedin a unit 108 at the subscriber site for example a costumer premiseequipment (CPE) such as a modem, router or any other gateway which mayalso be integrated in other devices such as a personal computer ornotebook.

The first transceiver unit 102 a includes a first transmitter 112 a anda first receiver 114 a coupled to the sub-scriber line 106. The secondtransceiver unit 102 b includes a second transmitter 112 b and a secondreceiver 114 b coupled to the subscriber line 106. For coupling of thetransmitters and receivers each of the transceiver units may comprise acoupling interface such as hybrid networks etc.

A first controller 110 a may be provided to provide controlling andcoordination functions for transceiver unit 102 a. Furthermore, a secondcontroller 10 b may be provided at the subscriber site to providecontrolling and coordination functions for transceiver unit 102 a.

While FIG. 2 shows the controllers 110 a and 110 b integrated with arespective one of transceiver units 102 a and 102 b, it is to beunderstood that the controllers 110 a and 110 b may be provided separatefrom the respective transceiver unit. It is further to be understoodthat components and entities shown may be implemented in hardware,software, firmware or any combinations thereof.

Furthermore, while FIG. 2 shows only one subscriber line to a remotesubscriber, it is to be understood that more than one transceiver unit102 a may be implemented in unit 104. Furthermore, as will be describedin more detail below, two or more subscriber lines may be bonded toprovide higher data rate to a subscriber.

Referring now to FIG. 3, an exemplary operation for providingretransmission is shown.

In a step S10 a data packet such as an Ethernet packet is received atthe first transceiver unit 102 a, for example from a backbone network.The data packet is separated in a plurality of data fragments at S20.For each of the plurality of data fragments an identification isprovided at S30. Then, at S40 the plurality of data fragments aretransmitted from the first transceiver unit 102 a to the secondtransceiver unit 102 b. At S50, a request for retransmission comprisingone or more identifications to indicate corrupt data fragments istransmitted from the second transceiver unit 102 b to the firsttransceiver unit 102 a. The request for retransmission at the firsttransceiver unit is processed at S60 to identify one or more datafragments based on the one or more identifications. Finally, at S70 theone or more identified data fragments are retransmitted.

It is to be noted that the data packet received at the first transceiverunit can be a data packet of variable length such as an Ethernet packet.According to embodiments, each data fragment may be processed betweenS30 and S40 to provide 64/65 octet encapsulation. The separating of thedata packet (S20) and the providing of identification for each datapacket (S30) may be implemented by processing the data packet between a64/65 octet encapsulation sublayer and a data link layer as will bedescribed in more detail below.

Furthermore, according to embodiments, distributing of the datafragments to a plurality of subscriber lines based on the data fragmentidentification may be provided for implementing bonding functionalities.It is to be noted that a synergetic effect may be provided here by theuse of the data fragment identification for identifying the fragments inbonding as well as in retransmission. Furthermore, other functionalitiesmay be shared between bonding and retransmission entities. The datafragment length may be variable and may for example be determined duringinitialisation or dynamically during normal operation. The data fragmentlength may have in an embodiment a minimum size of for example 32 bytes,64 bytes, 128 bytes, 256 bytes, 512 bytes etc. In other embodimentsother minimum fragment sizes may be implemented.

According to embodiments, a service specific retransmission may beprovided by multiplexing a first data stream associated with a firstservice type, a second data stream associated with a second service typeand a third data stream associated with retransmission data. Embodimentsrelated to the service specific retransmission will be described in moredetail below.

Furthermore, a packet start identifier may be provided in one of thedata fragments. Similar, a packet end identifier may be provided in oneof the data fragments. The packet start and packet end identificationcan be used to provide error detection for example by using CRC (cyclicredundancy check) methods such as CRC 16.

In the following, specific features of retransmission embodimentsrelated to the retransmission data unit, error detection, theretransmission request channel, service specific retransmission and theclassification of the retransmission within the layer model aredescribed. It is to be noted that the features described below may becombined in various ways in order to implement various embodiments.

Retransmission Data Unit

If a bonding sublayer PAF is implemented in the DSL system, afragmentation function is already provided with a configurable fragmentsize to construct fragments for distribution on links of a bondinggroup. Such fragments can be seen also as basic retransmission dataunits. So in case of retransmission and non-bonded links, the PAFfragmentation can be reused for building retransmission data units andin case of retransmission with bonded links, the PAF fragmentationbuilds fragments which are also retransmission data units.

According to embodiments, the fragment size configuration may beextended in such a way that it is not static any longer and to adapt thesize dynamically dependent on the current noise scenarios if impulsenoise measuring is done at the far-end and if this information istransferred to the retransmission & bonding sublayer transmitter.

It is to be noted that also the static fragment configuration size rangewhich is in existing systems between 64 and 512 bytes could be extendedfor the need of retransmission.

FIG. 6 a shows a conventional fragment with a PAF header of 16 bitsincluding SOP (start of packet) and EOP (end of packet) bits as well asthe sequence number bits SN (14 bits) provided by the PAF fragmentationof the bonding sublayer.

FIG. 6 b shows the modification of the fragment according to oneembodiment. A RTH field (retransmission header field) is prependedcontaining one additional byte (8 bits). The RTH field may be used forproviding retransmission specific information such as for indicatingwhether the data in the fragment data field is retransmitted data, toindicated how many times the data has been retransmitted (retransmissiondata repetition indication), the marking of different data streamsaccording to the different categories (priority) and indication ofretransmission sublayer specific data such as whether the fragment is aspecial idle fragment or not.

Error Detection

The bonding sublayer PAF offers the functionality of fragmentation witha fragment header consisting of sequence numbering via 14-bit SID andpacket boundary indication via the two bits StartOfPacket, EndOfPacketand fragment CRC-16 protection is supported by TPS-TC. This is neededfor reordering and reassembly. This functionality can be reused forerror detection and generation of retransmission requests. It is to benoted that the above functionalities are for example described in FIG.61-10 of IEEE 802.3 standard.

In case of non-bonded links and if the link is error-free, the receiversees for a current received fragment that this identification SID is theidentification SID+1 of the last received fragment.

If a noise impulse or other noise occurs, the receiver can detect afterthe end of noise impulse that SIDs are missing since then SIDcurrent isnot equal SIDlast+1.

In other embodiments, the receiver can detect the noise situation fromthe FEC (forward error correction) evaluation immediately and start aretransmission request immediately for all fragments that are expectedduring the time of disturbance. Here the receiver can notify thetransmitter about the situation by indicating which packet was the lastcorrectly received and how long the stream of bit errors continued afterthat. It is up to the transmitter to decide whether and which fragmentsneed to be retransmitted based on this information.

In case of bonded links, the incrementing by one can be supervised bythe receiver only after the reordering process but this may provide aretransmission request delay in dependence of the link differentialdelay. This would be solvable if the retransmission sublayer transmitterstores the information which SID has been distributed to which link ofthe group and if the retransmission sublayer receiver transfers in caseof errors the information about link number, current received SID andlast valid received SID on the corresponding link before the error sothat then the retransmission sublayer transmitter knows what it has toretransmit.

If the retransmission sublayer receiver gets a CRC errored fragment suchas a CRC-16 errored fragment it can discard this fragment and knows thatthe link is not error-free anymore.

If the error is longer than three 65-byte TPS-TC structures so that all3 structures are not valid the TPS-TC receiver may transfer to anout-of-synchronization (out-of-sync) state and will not forward any datavia gamma interface until it is again in synchronization (sync state).So if more than three 65-byte structures are needed for a fragment itcan occur that the sublayer above the TPS-TC receiver does not receive aCRC-16 errored fragment.

According to one embodiment, the retransmission sublayer receivermonitors the TPS-TC receiver regarding the synchronization state, i.e.supervision by control plane.

According to another embodiment, the receiver TPS-TC layer generates anOAM packet containing the information about a state transition from syncto out-of-sync which can be received by the retransmission sublayerreceiver.

Retransmission Request Channel

In the following exemplary embodiments for a retransmission requestchannel (RRC) are described.

According to one embodiment, a dedicated latency path and bearer channelmay be provided. This allows the use of an optimized transfer format. Itcan be defined such that a retransmission request consumes only a fewbytes, e.g. 6 bytes. Then the retransmission request sublayer shouldtransfer retransmission requests directly to the PMS-TC sublayer.

According to another embodiment, the existing TPS-TC OAM channel may beused for transmitting retransmission requests. If the OAM channel isused, the full line rate (a much higher bandwidth as 64 Kbit/s) can bereserved for the short time when the retransmission request is inserted.

The bonding OAM insertion buffers and bonding OAM extractfilters/buffers can be reused from the bonding sublayer. It is to benoted that the PAF OAM function BACP is similar to a mechanism which isused in case of ATM bonding.

Reduction of the waiting time for the retransmission-request insertiondue to current packet processing is to be considered. It may be possiblethat the insertion of a retransmission OAM packet with a retransmissionrequest has to wait for a just started processing of an Ethernet packetwith 1500 bytes. To reduce this delay, several techniques describedbelow may be used.

According to a first technique, fragmentation and sequence numberingcould be used for both line directions, also if this would be notrequired for non-bonded links with unidirectional retransmission, andthe fragment size is configured to the smallest possible value.

According to a second technique, preemption is used with priority ofretransmission OAM packets over other packets.

Furthermore, to keep the transfer time of a retransmission requestsmall, the 64/65-octet TC sublayer operation mode “short packets” can beused which allows packets smaller than 64 bytes.

In some embodiments, noise detection may be implemented. Theretransmission sublayer at the receiver site may detect the start of anoise impulse and may generate the retransmission request containing thelast valid received sequence number (LastValidSN). The retransmissionrequest may be generated and transferred repeatedly as long as noretransmission data has been received at the receiver.

According to one embodiment, the retransmission request channel may beprovided by the additional retransmission header RTH described abovewith respect to the retransmission data unit. In this case, theadditional retransmission header RTH contains information of theretransmission request such as the last valid received sequence number.Furthermore, rate decoupling may be used in the transmission directionof the retransmission request (upstream) to allow transfer ofretransmission requests at any time independent whether user data isavailable for transmission or not.

According to one embodiment, fragmentation and sequence numbering isprovided for both line directions also if this would not be required fornon-bonded links with unidirectional transmission and the fragment sizedis configured to a small size for example 64 bytes in order to avoidlong waiting times for the retransmission request.

In the retransmission request channel, an extension RTHe (retransmissionheader extension) of for example one byte may be added to the fragmentshown in FIG. 6 b in order to allow the inclusion of the last validreceived sequence number SN as shown in FIG. 6 c when a retransmissionrequest is transferred in the fragment. One bit of the retransmissionheader RTH may be used to indicate that the fragment contains theextension (i.e. that RTHe in FIG. 6 c follows) and the bits of the RTHand RTHe may be used to contain the last valid received numberLastValidSN which may for example include 14 bit.

Service Specific Retransmission

According to embodiments, the following services or classes of data maybe distinguished to take a service specific retransmission into account.

A first class of data referred to as class A is related to delaysensitive services which need no retransmission such as VoIP, gamingapplication; service with low bandwidth; service should not be delayedby retransmission of other services.

A second class of data referred to as class B is related to high qualityservice such as IPTV. For theses services which are relaxed on delayretransmission is provided.

A third class of data which is referred to as class C is related to Besteffort service such as WWW browsing, FTP download. These services arenot critical on delay and may not necessarily require retransmission.

Exemplary Requirements for a service specific retransmission will bedescribed below.

According to an embodiment, retransmission is applied only for the highquality service and not for the other services. On top of theretransmission protected service, i.e. net data rate minus high qualityservice rate, all available line bandwidth (data transmission rate) canbe used for forced insertion of retransmission data. According toembodiments, neither class B, C service data nor retransmission data ofthe high quality service may delay the delay sensitive data of class A.In other words, Class A transmission is strictly prioritized over allother services and over retransmission.

Several embodiments can be implemented based on the above mentionedservice specific retransmission.

According to an embodiment, two latency paths may be used with onebearer channel each. This would be the dual latency case since then onelatency path (bearer channel) will be setup for high impulse noiseprotection and the other latency path (bearer channel) will be setup fordelay sensitive data. But the delay sensitive service allocates alwaysline bandwidth, also if this service is off.

Another embodiment which will be described in more detail with respectto FIGS. 4 a and 4 b includes the usage of one latency path with onebearer channel but 2 channels between the retransmission sublayer of thetransmitter and the next higher sublayer and a strict prioritymultiplexer in the retransmission sublayer with delay sensitive servicedata from the next higher sublayer as first priority input,retransmission data from internal retransmission buffer as secondpriority input, other service data from the next higher sublayer asthird priority input. In this case, no fixed line rate is allocated forthe delay sensitive service and all available line bandwidth can be usedfor retransmission if the delay sensitive service is off.

FIG. 4 a shows now a first implementation of a queuing block or queuingentity 200 located above the bonding distribution sublayer.

As can be seen in FIG. 4 a, a data link entity 202 is coupled to afragmentation entity 204 provided to separate a data packet transferredfrom data link entity 202 into a plurality of fragments. A firstidentification entity 206 a associated with a first channel related toclass A services and a second identification entity 206 b associatedwith a second channel related to class B services are coupled to thefragmentation entity 204. The first and second identification entitiesprovide a sequence number for the plurality of data fragmentstransferred to each identification entity.

A priority multiplexer 208 comprises a first queue 208 a for class Aservices coupled to the first identification entity and a second queue208 b for class B and class C services coupled to the secondidentification entity 206 b.

Data from data fragments provided to the second queue are processed by aprocessor entity to determine whether a retransmission protection isneeded for the data as indicated by reference number 210. If it isdetermined that the data is to be protected by retransmission, the datais transferred to a retransmission buffer 214 after receiving linkinformation from a bonding distribution layer 212 to which themultiplexer 208 is coupled for distributing the received data fragmentsto communication links (subscriber lines) of the DSL system. The linkinformation may for example include information whether impulse noise iscurrently present on one or both of the communication links.

The retransmission buffer 214 is coupled to a third queue 208 c of themultiplexer 208 to retransmit the identified corrupt data fragments incase a retransmission is requested.

As indicated in FIG. 4 a, the three queues 208 a, b and c are strictlyprioritized such that data in queue 208 a is prioritized over data inqueue 208 c and data in queue 208 c is prioritized over data in queue208 b.

The data fragments from the queues are multiplexed according to theabove described priority scheme to the bonding entity 212. The bondingentity provides distributes the data among the bonded subscriber lines.Thus, data fragments intended to be transmitted over a first subscriberlines are transferred to a first TPS-TC entity 216 a associated with thefirst subscriber line and data fragments transmitted over a secondsubscriber line are transferred to a second TPS-TC entity 216 bassociated with the second subscriber line.

While FIG. 4 a shows only the TPS-TC layer, it is to be understood thatfor each of the subscribers lines layers and PMS-TC layer and PMD layersmay be provided. It is to be noted that the basic data chunks forprocessing are the data fragments as provided from the fragmentationentity.

FIG. 4 b shows a queuing if the queuing is located below the bondingdistribution sublayer.

As shown in FIG. 4 b, a first distribution entity 112 a for distributingthe priority class A data fragments to the subscriber lines and a seconddistribution entity 112 b for distributing the other data fragments,i.e. the priority class B/C data fragments to the subscriber lines arecoupled to the respective identification entities 206 a and 206 b.

For each subscriber line, a respective queuing entity 200 a and 200 b isprovided similar to the queuing entity shown in FIG. 4 a. Howeverdistinguished from FIG. 4 a, since the queuing entity is provided foreach subscriber line, transferring of line specific information is notrequired in the embodiment according to FIG. 4 b. Each of the bondingdistribution entities 206 a and 206 b has one output for distributingthe respective data fragments in accordance with the priority scheme tothe respective queues.

In the above, the queue 208 b gets high quality service data as well asbest effort service data so a differentiating factor is provided in anembodiment. A third channel between retransmission sublayer and the nexthigher sublayer may be implemented to provide separation of these data.This would require 3 interface addresses per DSL line if the next highersublayer is located in a different device.

According to one embodiment, a dedicated bit in the packet/fragment maybe used to indicate the service to be protected by retransmission. Thisinfo bit may be transferred also in the fragments because the far-endretransmission sublayer, i.e. the retransmission sublayer at thereceiver sees only one data stream. This sublayer has to queue theretransmission protected service data while waiting on retransmissiondata und may not queue other service data. Today this information isalready available in the VLAN tag of Ethernet packets. The fragmentationfunction could map this information via one special bit into thegenerated fragments.

For Class A service data, delay in the receiver due to a commonreordering entity for all service data is avoided, in one embodiment.Two sequence numbering and reordering entities may be used then, one forclass A service data and one for all other service data. Fordistinguishing between the two entities, one bit in the fragment headercan be used.

According to one embodiment, the differentiating factor may be the VLANtag prio field of Ethernet packets. In case of non-bonding application,the fragmentation is done by the retransmission sublayer transmitter andVLAN tag prio field evaluation can be done before fragmentation. In caseof bonding application, the fragmentation is done by the bondingsublayer transmitter and the retransmission sublayer transmitterevaluates the start of packet flag in the fragment header since thisfragment contains the VLAN tag prio field. This VLAN tag prio fieldinformation can be transferred to the far-end retransmission sublayer atthe receiver via bits in RTH. The data stream classification can be donevia different VLAN tag prio values. The relationship between VLAN tagprio and data stream class is communicated from the upper layers (datalink or higher layers) to layer 1 (PHY layer) before user traffic ispermitted.

Retransmission Data Insertion

In the following, embodiments of Retransmission Data insertion aredescribed. In case of bonded links and if the bonding sequence number(SN) is used also for retransmission, the SN increments consecutively onbonding group level but not on link level. This is addressed in oneembodiment if the retransmission sublayer transmitter stores the linkspecific transmission sequence order of SNs.

The transmitter gets from the far-end the information about the lastvalid received SN. It may stop then the sending of theby-retransmission-to-be-protected data stream for the time of configuredimpulse noise length INPMIN which may be correctable by retransmission.After this waiting time, it may retransmit the data units of the to-beprotected data stream of this link which has been sent fromLastValidSN+1 to the last sent SN when receiving the retransmissionrequest. After insertion of retransmission data, the normal data streamcan be continued.

For this retransmission principle, the retransmission sublayertransmitter should be aware of line data at any point of time. Thereforerate decoupling with “special idle fragments” as mentioned above may bedone in the retransmission sublayer transmitter and the sequencenumbering may be extended so that also the “special idle fragments” areincluded in the sequence numbering scheme. Identification of “specialidle fragments” can be done via a bit in RTH. Extension of sequencenumbering for “special idle fragments” can be done via bits in the idlefragment data. It can contain the 14-bit SN of the last user datafragment and an additional 14-bit SN which contains the information howmany idle fragments has been sent between the last user data fragmentand the current idle fragment.

Retransmission in the Layer Model

The following FIGS. 5 a to 5 d show two embodiments of arrangingretransmission sublayer functions in a layer model.

FIGS. 5 a and 5 b show an embodiment of a protocol stack for bondingwith two links and retransmission for downstream data where queuing andforwarding of the retransmission sublayer transmitter with insertion ofretransmission data is located above the distribution of the bondingsublayer transmitter. According to this embodiment, line specific errordetection is provided in the retransmission sublayer of the receiver.Furthermore, bonding OAM insertion function is used also forretransmission request insertion and a line specific retransmissionrequest is transported over all bonded links.

In more detail, FIG. 5 a shows a protocol stack for a receiver andtransmitter at the Central Office site while FIG. 5 b shows the protocolstack at the subscriber site (remote site). The protocol stack 300 a ofthe receiver at the Central Office site comprises a bonding andretransmission sublayer between the gamma interface and the data linklayer (not shown). The bonding and retransmission sublayer comprises afragmentation entity which may correspond to the fragmentation entity204, an identification entity (sequence numbering) which may correspondto the identification entity 206, a queuing and forwarding entity and adistribution entity which may correspond to the bonding distributionentity 212. It is to be noted that the queuing and forwarding entity maycorrespond to the service dependent queuing entity 200 of FIG. 4 a ormay be a non-service dependent queuing entity.

In the TPS-TC sublayer, a CRC-16 entity with a bonding OAM entity fortransmitting bonding information over an OAM channel is provided.Furthermore, the TPS-TC sublayer comprises a rate decoupling entity anda 64/65 octet encapsulation entity. The rate decoupling entity fillseach TPS-TC encapsulation structure (in case of 64/65-octet TPS-TC itfills each 65-byte structure) with idle bits if data fragments are notfully occupied with user data. If a data fragment is fully occupied withidle bits, indication can be provided to the data fragment in order toavoid unnecessary retransmission of the non-useful data. The CRC-16calculation entity provides CRC-16 calculation based on packet start andpacket end identification provided in some of the data fragments. The64/65 octet encapsulation entity provides 64/65 octet encapsulation asis known to a person skilled in the art.

In the PMS-TC sublayer, a framing entity, an interleaving entity isprovided together with a PMS-TC layer OAM entity to provide OAM channelcommunication at PMS-TC level. Finally a PMD sublayer as explained withrespect to FIG. 1 is provided.

As can be sheen in FIGS. 5 a and 5 b, each of the above describedentities of the PMS-TC and TPS-TC sublayers are provided for each of thesubscriber lines.

At the subscriber site, a protocol stack 302 a having the reversesequence of the protocol stack is provided in order to implement areceiver protocol stack. It is to be understood for a person skilled inthe art that functionalities such as the interleaver framing and ratecoupling are replaced at the receiver site by the complementaryfunctionality.

Furthermore, it is to be understood that a transmitter protocol stack300 b similar to the protocol stack 300 a may be implemented at thesubscriber site. However, since the retransmission protection is onlyprovided for downstream direction, no specific retransmissionfunctionality is implemented at the protocol stack 300 b.

As can be seen in FIG. 5 b, a line specific error detection entity isprovided at the receiver protocol stack 302 a of the subscriber site todetect corrupt received data fragments. By using the identificationprovided by the identification entity at the Central Office site, theline specific error detection entity is capable of identifying thecorrupt data fragments and transfers the identification information tothe bonding OAM data entity of the transmitter protocol stack at thesubscriber line. As can be seen in FIG. 5 b, the information may beprovided from the protocol stack for each of the subscriber lines to theOAM data entities of the transmitter protocol stacks for each subscriberline to allow transmitting of a retransmission request including theidentification information over both subscriber lines back to theCentral Office. This allows a more robust transmission of theretransmission request from the subscriber to the Central Office. At theCentral Office, a receiver protocol stack 302 b is implemented similarto the receiver protocol stack 302 a. However, since in the describedembodiment only downstream data, i.e. data transmitted from the CentralOffice to the subscriber, is retransmission protected, a line specificerror detection is not implemented at the receiver protocol stack at theCentral Office. At the Central Office, the retransmission request isprocessed by the bonding OAM entity. The bonding OAM entity transfersthe identification information to the queuing and forwarding entity inthe bonding and retransmission sublayer in order to start theretransmitting of the data fragments which are identified as corruptlyreceived.

While FIGS. 5 a and 5 b show the queuing and forwarding functionalityabove the bonding distribution functionality, FIGS. 5 c and 5 d shows anembodiment for bonding with two links and retransmission for downstreamdata wherein the queuing and forwarding of the retransmission sublayertransmitter with insertion of retransmission data is located below thedistribution of the bonding sublayer transmitter. FIG. 5 c shows theprotocol stack at the Central Office site and FIG. 5 d shows theprotocol stack at the subscriber site (remote site). In this embodiment,a line specific retransmission request is transported over the effectedline in opposite direction, i.e. a pure link specific retransmissionscheme is implemented. Distinguished from the embodiment of FIGS. 5 aand 5 b, the retransmission request is only retransmitted over one ofthe subscriber lines, i.e. the retransmission request is transmittedover the same subscriber line on which the respective data fragmentshave been transmitted.

It is further to be noticed that in the embodiment according to FIGS. 5c and 5 d, since the queuing is implemented below the distribution, aqueuing entity is provided for each of the respective subscriber linessimilar to the provision of queuing entities for each subscriber line inthe embodiment described with respect to FIG. 4 b.

FIGS. 7 a and 7 b show a further embodiment of a protocol stack. In thisembodiment, the bonding sublayer and the retransmission sublayer areseparated. FIG. 7 a shows the protocol stack at the Central Office site.FIG. 7 b shows the protocol stack at the subscriber site (remote site).

A rate decoupling is provided in this embodiment for the implementationof the separate bonding sublayer and retransmission sublayer. Since therate decoupling is provided below the bonding sublayer, the idlefragments are inserted/removed in a sublayer below the bonding sublayer.Therefore, the bonding sublayer is not capable of providing sequenceinformation numbering for idle fragments. In order to allow sequencenumber identification also for idle fragments, the special category ofidle fragments is provided which are hereinafter referred to as specialidle fragments. These special idle fragments are inserted and removed inthe retransmission layer provided between a bonding layer and the TPS-TClayer. The special idle fragments are not detected as idle fragments bythe TPS-TC layer at the far-end receiver such that the retransmissionsublayer at the far-end can receive these special idle fragments,identify them, evaluate the information contained therein, for examplethe sequence number identification of the idle fragment, and discardthese special idle fragments in order to prohibit the further transferof the special idle fragments to the bonding sublayer.

In case of bonded links and if the bonding sequence number SN is usedalso for retransmission, the SN increments consecutively on bondinggroup level but not on link level. Therefore, the retransmissionsublayer at the transmitter site may store the link specifictransmission sequence order of SNs.

The transmitter gets from the far-end the information about the lastvalid received SN. It may stop then the sending of theby-retransmission-to-be-protected data stream for the time of configuredimpulse noise length INPMIN which may be correctable by retransmission.After this waiting time, it may retransmit the data units of the to-beprotected data stream of this link which has been sent fromLastValidSN+1 to the last sent SN when receiving the retransmissionrequest. After insertion of retransmission data, the normal data streamcan be continued.

For this retransmission principle, the retransmission sublayertransmitter may be aware of line data at any point of time. Thereforerate decoupling with “special idle fragments” as mentioned above may bedone in the retransmission sublayer transmitter and the sequencenumbering may be extended so that also the “special idle fragments” areincluded in the sequence numbering scheme.

Identification of “special idle fragments” can be done via a bit in RTH.Extension of sequence numbering for “special idle fragments” can be donevia bits in the idle fragment data. It can contain the 14-bit SN of thelast user data fragment and an additional 14-bit SN which contains theinformation how many idle fragments has been sent between the last userdata fragment and the current idle fragment.

According to one embodiment, the special idle fragments are used fortraining or determining one or more parameters of repetitive noise suchas REIN (repetitive electrical impulse noise) parameters. The one ormore parameters may then be used to determine time periods during whichthe repetitive noise is expected. During the determined time periods ofthe repetitive noise, no user data may be transmitted. According to oneembodiment, instead of user data the special idle fragments aretransmitted during the determined time periods.

To determine the parameters of repetitive noise, a plurality of specialidle fragments are repeatedly transmitted from the transmitter to thereceiver, wherein each of the special idle fragments comprising asequence number. One or more sequence numbers of corrupted special idlefragments are identified at the receiver and one or more parameters ofthe repetitive noise based on the identified sequence numbers aredetermined. According to one embodiment, information related to a startand end of a repetitive impulse is transmitted from the receiver to thetransmitter and the parameters of the repetitive noise are determinedbased on the transmitted information.

According to one embodiment, the retransmission sublayer at thetransmitter site applies rate decoupling with special idle fragments andthe sequence numbering is extended to these special idle fragments andthe receiver informs the transmitter about the end of noise via firstvalid received sequence numbering. Then, the transmitter can detect inthe first seconds after link startup whether repetitive noise exists ornot. The user data stream will be enabled in the higher layers a bitlater after link startup so that in the first seconds after linkstartup, there will be only special idle fragments on the line. In caseof repetitive noise, the receiver will communicate a predeterminednumber of times, for example 100 times, a start of noise and end ofnoise message during the first second after link startup so that thetransmitter can detect the periodicity and length of corrupted data. Dueto this knowledge, the transmitter can from now on prevent that userdata will be transmitted during the time of repetitive noise impulsesvia insertion of special idle fragments which don't need to beretransmitted. According to one embodiment, this user data preventionmay be adapted dynamically during showtime, e.g. every 5 seconds.

With the above described determining of repetitive noise parameters andpreventing of transmission during expected REIN periods, theretransmission scheme can be used for example when a combination ofrepetitive noise (repetitive noise impulses of up to 5 symbols every 10ms) and non-repetitive noise such as noise impulses with long width (ofup to 64 symbols) with a long time distance between the noise impulsesoccurs. The above embodiment of preventing transmission of user data bytransmitting the special idle fragments allows an efficientretransmission with a predetermined retransmission waiting time (minimumnumber of symbols the transmitters waits until retransmitting the data)longer than a period of the repetitive noise.

As described above, according to embodiments, the following data streamscan be differentiated:

-   -   1) Class B: High quality service; retransmission needed (IPTV;        delay not very critical)    -   2) Class a: Delay Sensitive Service; No Retransmission needed        (VoIP, gaming application; service with low bandwidth; service        should not be delayed by retransmission of other services    -   3) Class C: best effort service; no retransmission needed (WWW        browsing, FTP download; delay not critical).

Requirements for a data stream specific retransmission could be asfollows:

-   -   i) Apply retransmission only for the high quality service and        not for the other services    -   ii) All available line bandwidth on top of the retransmission        protected service, i.e. net data rate minus high quality service        rate, to be used for forced insertion of retransmission data,    -   iii) But retransmission data of the high quality service may not        delay the delay sensitive data.

According to one embodiment, usage is made of one latency path with onebearer channel but 2 channels between the retransmission sublayertransmitter and the next higher sublayer and a strict prioritymultiplexer in the retransmission sublayer with delay sensitive servicedata from the next higher sublayer as first priority input,retransmission data from internal retransmission buffer as secondpriority input, other service data from the next higher sublayer asthird priority input. No fixed line rate is allocated for the delaysensitive service and iii) can be fulfilled if the delay sensitiveservice is off. The third priority input gets high quality service dataas well as best effort service data so a differentiating factor isneeded.

The differentiating factor is the VLAN tag prio field of Ethernetpacket. In case of non-bonding application, the fragmentation is done bythe retransmission sublayer transmitter and VLAN tag prio fieldevaluation can be done before fragmentation. In case of bondingapplication, the fragmentation is done by the bonding sublayertransmitter and the retransmission sublayer transmitter has to evaluatethe start of packet flag in the fragment header because this fragmentcontains the VLAN tag prio field.

This VLAN tag prio field information can be transferred to the far-endretransmission sublayer receiver via bits in RTH.

The data stream classification can be done via different VLAN tag priovalues. The relationship between VLAN tag prio and data stream class maybe communicated from the upper layers to layer 1 (PHY layer) before usertraffic is permitted.

One embodiment of a layer model of the above described retransmissionscheme with separated bonding and retransmission sublayer is shown inFIGS. 7 a and 7 b. As can be seen, the bonding layer providesfragmentation, sequence numbering and distribution functionality for theuser data above the retransmission sublayer. The retransmission sublayerincludes the prepending of the retransmission header wherein the RTHfield as shown in FIG. 6 b is added. Furthermore, rate decoupling isprovided wherein the special idle fragments are inserted in thetransmitter protocols stacks 300 a and 300 b or are removed in thereceiver protocol stacks 302 a and 302 b. It is to be noted that at theprotocol stack 302 a of the receiver at the subscriber site, a removalof rate decoupling data (normal idle data) is provided in the TPS-TClayer. However, this functionality does not remove the special idlefragments which are transferred to the retransmission sublayer and areonly removed after the CRC check and error detection and identifying ofthe sequence number of a corrupt idle fragment. After a corrupt fragmentor a corrupt special idle fragment has been detected, the sequencenumber of the last valid fragment is mapped in the fragment headerextended by the RTH and RTHe fields (compare for FIG. 6 c) at thetransmitter protocol stack 300 b and transmitted to the receiver at theCentral Office site. The protocol stack at the Central Office sitedemapps the sequence number in the fragment header and provides thisinformation to the RT sublayer of the transmitter protocol stack 300 aat the CO site to start retransmission. It is to be noted thatretransmission may start after waiting a predetermined time period asdescribed above.

While the above describes embodiments with a bonding sublayer, it is tobe noted that in other embodiments the functionalities such as sequencenumbering, fragmentation, and reassembly can be included in theretransmission sublayer without providing the bonding sublayer.

In the above description, embodiments have been shown and describedherein enabling those skilled in the art in sufficient detail topractice the teachings disclosed herein. Other embodiments may beutilized and derived there from, such that structural and logicalsubstitutions and changes may be made without departing from the scopeof this disclosure.

This Detailed Description, therefore, is not to be taken in a limitingsense, and the scope of various embodiments is defined only by theappended claims, along with the full range of equivalents to which suchclaims are entitled.

Such embodiments of the inventive subject matter may be referred toherein, individually and/or collectively, by the term “invention” merelyfor convenience and without intending to voluntarily limit the scope ofthis application to any single invention or inventive concept if morethan one is in fact disclosed. Thus, although specific embodiments havebeen illustrated and described herein, it should be appreciated that anyarrangement calculated to achieve the same purpose may be substitutedfor the specific embodiments shown. This disclosure is intended to coverany and all adaptations or variations of various embodiments.Combinations of the above embodiments, and other embodiments notspecifically described herein, will be apparent to those of skill in theart upon reviewing the above description. It is further to be understoodthat the various methods disclosed in this specification and the claimscan be implemented in devices having means or circuit componentsconfigured to enable the corresponding method steps.

It is further to be noted that specific terms used in the descriptionand claims may be interpreted in a very broad sense. For example, theterms “circuit” or “circuitry” used herein are to be interpreted in asense not only including hardware but also software, firmware or anycombinations thereof. The term “data” may be interpreted to include anyform of representation such as an analog signal representation, adigital signal representation, a modulation onto carrier signals etc.Furthermore the terms “coupled” or “connected” may be interpreted in abroad sense not only covering direct but also indirect coupling.Transmitter and receiver as used herein may in some embodiments be atransmitter or receiver device such as a modem and in other embodimentsbe only a single chip such as a baseband chip.

The accompanying drawings that form a part hereof show by way ofillustration, and not of limitation, specific embodiments in which thesubject matter may be practiced.

The Abstract of the Disclosure is provided to comply with 37 C.F.R.§1.72(b), requiring an abstract that will allow the reader to quicklyascertain the nature of the technical disclosure. It is submitted withthe understanding that it will not be used to interpret or limit thescope or meaning of the claims. In addition, in the foregoing DetailedDescription, it can be seen that various features are grouped togetherin a single embodiment for the purpose of streamlining the disclosure.This method of disclosure is not to be interpreted as reflecting anintention that the claimed embodiments require more features than areexpressly recited in each claim. Rather, as the following claimsreflect, inventive subject matter lies in less than all features of asingle disclosed embodiment. Thus the following claims are herebyincorporated into the Detailed Description, where each claim may standon its own as a separate embodiment. While each claim may stand on itsown as a separate embodiment, it is to be noted that—although adependent claim may refer in the claims to a specific combination withone or more other claims—other embodiments include a combination of thedependent claim with the subject matter of each other dependent claim.

It is further to be noted that methods disclosed in the specification orin the claims may be implemented by a device having means for performingeach of the respective steps of these methods.

1. A method comprising receiving a data packet; separating the data packet in a plurality of data fragments; providing for each of the plurality of data fragments or for a group of the plurality of data fragments an identification; transmitting the plurality of data fragments from a first transceiver unit to a second transceiver unit; transmitting a request for retransmission from the second transceiver unit to the first transceiver unit, the request comprising one or more identifications; processing the request for retransmission at the first transceiver unit to identify one or more data fragments based on the one or more identifications; and retransmitting the one or more identified data fragments.
 2. The method according to claim 1, further comprising processing each data fragment to provide 64/65 octet encapsulation.
 3. The method according to claim 1, wherein the separating of the data packet and the providing of an identification is provided by a processing between a 64/65 octet encapsulation sublayer and a data link layer.
 4. The method according to claim 1, further comprising: distributing the data fragments to a plurality of subscriber lines based on the identification.
 5. The method according to any of claims 1, further comprising dynamically changing the length of the data fragments.
 6. The method according to claim 1, further comprising: multiplexing a first data stream associated with a first service type, a second data stream associated with a second service type and a third data stream associated with retransmission data.
 7. The method according to claim 1, further comprising: providing information indicating whether a fragment of the plurality of fragments is to be protected by retransmission or providing information indicating whether a group of fragments is to be protected by retransmission.
 8. The method according to claim 1, further comprising providing a rate decoupling functionality by transmitting idle fragments which are transparent to a TPS-TC layer of the first transceiver and the second transceiver or at least all TPS-TC sublayers hierarchically below the rate decoupling functionality.
 9. The method according to claim 1, further comprising determining one or more repetitive noise parameters, the one or more repetitive noise parameters determining time periods during which no user data is transmitted.
 10. The method according to claim 1, further comprising: transmitting from the second transceiver to the first transceiver a request for retransmission, the request for retransmission including the identification of the last correctly received data fragment or the identification of the last correctly received group of data fragments.
 11. A transmitter comprising: a fragmentation entity to separate a packet into a plurality of data fragments; an identification entity to provide for each data fragment or group of data fragments an identification; a retransmission entity to receive a retransmission request including at least one of the identifications of the data fragments from a remote transceiver unit.
 12. The transmitter according to claim 11, further comprising a TPS-TC entity to receive the data fragments with the identification and provide TPS-TC processing; and wherein the retransmission entity is configured to transfer to the TPS-TC entity one or more data fragments based on the at least one identifications received from the remote transceiver unit.
 13. The transmitter according to claim 11, further comprising a bonding entity for bonding a plurality of subscriber lines wherein the bonding entity is configured to distribute the data fragments to the plurality of subscriber lines.
 14. The transmitter according to claim 11, further comprising a rate decoupling entity, wherein the rate decoupling entity is configured to include idle fragments which are transparent to a TPS-TC layer or at least all TPS-TC sublayers hierarchically below the rate decoupling entity.
 15. The transmitter according to claim 11, further comprising a multiplexer, the multiplexer configured to multiplex a first data stream of data fragments associated with a first service type, a second data stream of data fragments associated with a second service type and a third data stream of data fragments associated with retransmission data.
 16. A receiver comprising a retransmission entity to receive data fragments, wherein each of the data fragments or a group of data fragments comprises an identification, wherein the retransmission entity is configured to provide indication of at least one corrupt fragment; and a request generation entity to receive the indication and to generate a retransmission request based on the identification and the indication of at least one corrupt data fragment or at least one corrupt group of data fragments.
 17. The receiver according to claim 16, wherein the retransmission entity is configured to receive the data fragments from a TPS-TC entity, the TPS-TC entity implementing at least one functionality of a TPS-TC sublayer for the received data fragments.
 18. The receiver according to claim 16, further comprising a CRC entity, the CRC entity providing an error detection based on a packet start identifier provided in at least a first fragment of the data fragments and a packet end identifier provided in at least a second fragment of the plurality of fragments.
 19. The receiver according to claim 16 wherein the receiver comprises a bonding entity, the bonding entity sharing at least one functionality with the retransmission entity.
 20. A DSL transmission system comprising: a first transceiver unit, the first transceiver unit comprising a fragmentation entity to separate a packet into a plurality of data fragments; a first identification entity to provide for each data fragment or a group of data fragments an identification; a first transmission entity to transmit the plurality of data fragments; and a first retransmission entity to receive retransmission requests and to identify at least one fragment based on the received retransmission request; a second transceiver unit, the second transceiver unit comprising a second retransmission entity to receive the plurality of data fragments and to provide indication of at least one corrupt data fragment; a request generation entity to receive the indication and to generate a retransmission request based on the indication and the identification; and a transmission entity to transmit the retransmission request to the first transceiver unit.
 21. The system according to claim 20, wherein the first transceiver unit further comprises a CRC entity to provide a packet start identifier in at least a first one of the data fragments and a packet end identifier in at least a second one of the data fragments and wherein the second transceiver further comprises a CRC entity to provide error detection based on the packet start and packet end identifier.
 22. The system according to claim 20, wherein the first retransmission entity is configured to transmit the data fragments to a first TPS-TC entity, the first TPS-TC entity implementing at least one functionality of a TPS-TC sublayer, and wherein the second retransmission entity is configured to receive the data fragments from a second TPS-TC entity, the second TPS-TC entity implementing at least one functionality of a TPS-TC sublayer.
 23. The system according to claim 20, wherein the first transceiver comprises a rate decoupling entity, wherein the rate decoupling entity is configured to include idle bytes in at least one of the TPS-TC encapsulation structures.
 24. A protocol stack for a DSL transmission system, the protocol stack comprising a retransmission functionality, the retransmission functionality being provided between a sublayer of a TPS-TC layer and a data link layer, the retransmission functionality having a fragment of a packet or a group of fragments of a packet as basic retransmission unit.
 25. The protocol stack according to claim 24, wherein the protocol stack is implementing a service specific retransmission functionality such that for a first class of services retransmission protection is provided and for a second class of services no retransmission protection is implemented. 